1 Field of the Invention
The invention relates to a process for manufacturing elastomeric tire components and more particularly tire components for motorvehicles.
2 Description of the Related Art
Generally speaking, a tire for motorvehicles comprises a carcass structure made up of one or more carcass plies of a substantially toroidal shape and having their axially opposite side edges in engagement with respective annular reinforcing elements usually referred to as “bead cores”, a tread band made of an elastomeric material at a radially outer position with respect to said carcass structure, a belt structure interposed between said carcass structure and said tread band and a pair of axially opposite sidewalls on said carcass structure, each of which covers a side portion of the tire radially extending between a so-called shoulder region of the tread band and a so-called bead located at the respective bead core.
It should be specified herein that in the present description and in the subsequent claims, the term “elastomeric material” is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Typically, such a composition also comprises additives such as, for example, a vulcanizing agent and/or a plasticizer. Thanks to the presence of the vulcanizing agent, such a material may be vulcanized by heating, so as to form the end product.
In the field of tire manufacture, it has been proposed to form elastomeric tire components by laying a continuous elongated element of a suitable elastomeric material onto a substantially cylindrical or toroidal support rotatable about its rotation axis. Such a continuous elongated element generally has a reduced size as compared with that of the final component to be obtained and is arranged on the rotatable support so as to form a plurality of consecutive coils arranged side by side and/or in overlapped relationship with one another.
It should be specified herein that in the present description and in the subsequent claims, the term “elastomeric tire component” is used to indicate all those components of the final tire, or parts thereof, which are constituted by an elastomeric material.
Non limitative examples of elastomeric tire components according to this definition are: the tread band; the sidewalls; the so-called liner, that is a thin layer of elastomeric material that, once vulcanization has been completed, will be airtight so as to ensure maintenance in use of the tire's inflating pressure; the so-called under-liner, interposed between the liner and the carcass plies; the under-belt inserts; the filling inserts of the annular reinforcing structures; the sidewall inserts of the so-called run-flat tires; the abrasion-resistant inserts externally applied close to one of the tire bead elements; or parts of any of these exemplary components.
In particular, when, as an example, the sidewalls and/or the tread band are realized in two or more distinct parts, each made of a specific elastomeric material, the term “elastomeric tire component” indicates each of the aforesaid parts of the sidewalls and/or of the tread band.
International patent applications WO 00/35666 and WO 01/36185, in the name of the present Applicant, teach that some of the tire components can be obtained by delivering an elongated element from an extruder and by suitably depositing this element on a support bearing the green tire being manufactured, said support being rotated about its own axis and moved with respect to the extruder by a robotized arm for obtaining a transversal deposition of the elongated element to form a plurality of circumferentially axially adjoined and/or radially overlapped coils that give rise to the tire component. The orientation and mutual-overlapping parameters of said coils are suitably managed so as to control the thickness of each a elastomeric tire component being made, based on a predetermined deposition scheme preset on an electronic computer.
Known from document GB 1,048,241 is a machine for laying down a layer of elastomeric material of varying thickness on a tire carcass and comprising a feeding head to apply a ribbon of elastomeric material to the carcass, means for setting the carcass in rotation about its axis for winding of a plurality of coils thereon when the carcass rotates with respect to the feeding head, means for moving the feeding head transversely of the carcass, from one side to the other of the circumferential median plane of the carcass, and means for automatically varying the transverse-movement amount for each winding revolution so as to vary the overlapping degree of the contiguous coils and consequently thickness of the layer formed on the carcass. In an appropriate version for making new tires, during formation of the tread band the carcass is mounted on a building drum and has a cylindrical right conformation.
EP 1 211 050 describes a method for extruding a tire rubber material by a positive displacement extruding system including as seen from an upstream side of the tire rubber, a screw extruder unit, a gear pump unit and an extrusion head unit with an extrusion nozzle, which are connected in series with each other. While the tire rubber is caused to flow through the extruding system, the temperature of the rubber material is measured and controlled to be within a predetermined temperature range.
EP 492,425 describes an extrusion system and a method for extruding strips of rubber compounds which are uniformly heated and mixed in an extruder. A control system regulates the speed of the extruder to provide a near constant pressure at the entrance port of the gear pump to precisely regulate the rate of extrusion of the compound from the extrusion head. The temperature of the rubber compound is maintained within a predetermined temperature range less than 100° C. Temperatures and pressures are said to be measured at the various other positions in the system as inputs for algorithms which are designed to induce changes in the speed of feed mixer during start-up, shutdown and steady state operations, to maintain the desired pressures, feed rates and temperatures throughout the entire system.
U.S. Pat. No. 6,468,067 discloses a composite extruding apparatus of rubber and a method of extruding unvulcanized rubber. The apparatus has a reduced screw length, whereby the material residue is reduced, and the temperature control is facilitated to prevent rubber scorching. The temperature control is said to be effected by an ordinary method.